A3-02 Expanding the Differential: Langerhans Cell Histiocytosisas as a Cause of Recurrent Pleural Effusion

Abstract

Langerhans Cell Histiocytosis (LCH) is a rare neoplastic disorder (0.07/million annually), characterized by clonal proliferation of CD1a+/CD207+ myeloid precursors forming eosinophilic granulomas and leading to multi-organ dysfunction. Pulmonary involvement, often linked to tobacco use, typically manifests as small nodules and irregular cysts sparing lung bases. Pleural effusion is an exceptionally rare presentation of LCH, generally confined to case reports. This report details a case of LCH in a former smoker presenting with recurrent pleural effusions. A 49-year-old man with no significant medical history presented to the ED with left flank pain. A CT abdomen/pelvis revealed left nephrolithiasis, an incidental peri-pancreatic mass (4.3 x 5 x 3.8 cm), and a left-sided pleural effusion. Subsequent CT chest identified asymmetric soft tissue density in the left chest wall over the 8th and 9th ribs, multifocal lytic bone lesions, a large left pleural effusion, and increasing left lower and upper lobe consolidation, raising suspicion for metastatic disease (Figure 1A). A chest wall mass biopsy confirmed LCH, positive for S100, CD1a, and CD68. Left thoracentesis showed an exudative effusion with reactive mesothelial and atypical cells (pleural cultures negative). Three weeks later, recurrent left pleural effusion necessitated placement of a tunneled pleural catheter. Biopsy of the peri-pancreatic mass also tested positive for LCH. A follow-up PET scan (Figure 1B) revealed multiple FDG-avid posterior left-sided rib lesions extending into intercostal musculature, left pleural effusion, and multiple left-sided lymphadenopathies. The patient was subsequently scheduled for outpatient chemotherapy with Cobimetinib. However, he presented to the ED with dyspnea, fevers, and reduced pleural drainage from the TPC. A CT chest demonstrated a large, now loculated, left pleural effusion (Figure 1C). Decreased pleural fluid glucose, despite negative cultures, suggested an infected pleural space. He was treated with antibiotics and intrapleural tPA-Dornase. Critically, left pleural fluid cytology (Figure 1D) immunostained for S100 and CD1a, confirming LCH involvement. LCH presents with variable clinical manifestations affecting bone, skin, pituitary glands, liver, spleen, lymph nodes, and lungs. Pulmonary involvement typically presents as cough and dyspnea with cystic and/or nodular changes on CT. Pleural effusions are rare in LCH and if present, warrant investigation for other etiologies. When secondary to LCH, the pathophysiology of effusion can stem from chylous obstruction, secondary infection, direct pleural involvement, or pneumothorax-related inflammation. While not always diagnostic, cytology was pivotal in identifying the LCH-related cause of pleural effusion in this case, highlighting its potential utility in complex presentations.

This abstract is funded by: None